Earlier police said it’s believed "there are around 40 casualties" who are being treated by ambulance crews.

East of England Ambulance Services said eight patients had been taken to the James Paget Hospital with asthma and breathing problems, but all were in a "stable condition".

A further 29, the service said, are being assessed and treated on site for "breathing problems, none of whom are thought to be in a serious condition".

It said three ambulance officers, five ambulances, two critical care paramedics and the Hazardous Area Response Team were in attendance.

The immediate area around the leak site has been evacuated, police said in a statement, and a 20 metre cordon has been put in place around the building "whilst emergency services deal with the incident".

Tom Cassidy, a spokesman for Haven Holidays, which runs the resort, told the Press Association that 40 people were originally treated by paramedics and 33 "walking wounded" were taken to three different hospitals as a "precaution". A three-year-old was among those taken to hospital.

He said: "There was a chemical leak in the swimming pool in the entertainment complex and it was evacuated while police and fire and rescue were on their way."

Wild Duck Holiday Park promises customers a 'relaxing time' on its website, and has facilities including a restaurant, play area, sports court and pools, including a seaside-themed outdoor pool.